When tumorigenic and non-tumorigenic cells are fused in culture, the resulting hybrid cells are usually non-tumorigenic. Loss of tumorigenicity is attributed to heritable factors within the non-tumorigenic cell which suppress tumor development. Several tumor suppressors including the retinoblastoma gene and p53 have been characterized and are of great interest to researchers and clinicians seeking to investigate and control cancer growth. Both the retinoblastoma gene and p53 have become candidates for the development of cancer therapeutics (Knudson, A. G. (1993) Proc. Natl. Acad. Sci. 90: 10914-21; Antelman, D. et al. (1995) Oncogene 10: 697-704; and Hamada, K. et al. (1996) Cancer Res. 56: 3047-54).
One of the genes which suppresses tumorigenesis, tsg101, was recently identified in mouse (Li, L. and S. N. Cohen (1996) Cell 85:319-329). Antisense RNA was used to disrupt transcribed genes throughout the genome of mouse 3T3 fibroblasts. Homozygous functional disruption caused oncogenesis, and the oncogenic cells, in turn, produced metastatic tumors in nude mice. Removal of the transactivating RNA allowed Li and Cohen (supra) to study and characterize genes with tumor suppressor activity.
Tsg 101 was identified using this methodology and cloned from a mouse NIH 3T3 cell cDNA library. The predicted protein has 381 amino acids; an alpha-helix domain which has identity with cc2; a stathmin interaction domain; a proline-rich region which precedes a leucine zipper motif; a zinc finger signature (residues 73-83); seven potential protein kinase C phosphorylation sites (11, 38, 85, 88, 215, 225, 357); five potential casein kinase II phosphorylation sites (38, 210, 249, 265, 290); two potential N myristoylation sites (55 and 156); and three potential N glycosylation sites (44, 150, 297). Oncogenesis was observed when the activity of tsg101 was knocked out by introducing a synthesized, tsg101 antisense RNA into native NIH 3T3 cells.
The zinc finger and leucine zipper motifs of tsg101 may allow the protein to function as a transcription factor; however, Li and Cohen (supra) suggest tsg101 may interact with stathmin (oncogene 18), a cytosolic phosphoprotein that functions in cell growth and differentiation. Stathimin is known to be phosphorylated in response to growth and differentiation factors during cell cycle transitions, embryonic development, T cell activation, and tissue regeneration. Stathmin expression increases in acute leukemia, highly malignant lymphoma and neuroblastoma and in cells overexpressing tsg101 (Li and Cohen, supra).
Mutations in tumor suppressor genes are a common feature of many cancers and often appear to affect a critical step in the pathogenesis and progression of tumors. Accordingly, Chang, F. et al. (1995; J. Clin. Oncol. 13: 1009-1022) suggest that it may be possible to use either the gene or an antibody to the expressed protein 1) to screen patients at increased risk for cancer, 2) to aid in diagnosis made by traditional methods, and 3) to assess the prognosis of individual cancer patients. In addition, Hamada et al. (supra) are investigating the introduction of p53 into cervical cancer cells via an adenoviral vector as an experimental therapy for cervical cancer.
Polynucleotides and polypeptides related to tsg101 satisfy a need in the art by providing compositions useful in the diagnosis, prevention, and treatment of cancer and autoimmune diseases.